Conformation analysis of the polypeptides in the thylakoid membrane.

The ultraviolet circular dichroism spectrum of a chloroplast fraction of Antirrhinum ma jus has recently been published The fraction was obtained from stroma-freed chloroplasts by ultrasonic treatment and fractioning centrifugation2-3. The spectrum shows extrema of ellipticity at 194 ( + ) , 208 ( ) and 222 ( —) nm. Thus it is similar to a protein with a considerable a-helix content. G R E E N F I E L D and F A S M A N 4 have calculated circular dichroism spectra for proteins of different conformations by linear superposition of reference spectra. These authors used poly-L-lysine in a, ß and random coil conformations for reference. A comparison with the spectra of G R E E N F I E L D and F A S MAN 4 shows that the spectrum of the fragments of the thylakoid membrane closely resembles that of a protein with 42 percent a-helix, 40 percent random coil and 18 percent ^-structure (Fig. 1). The biggest dif-